Transcript for Major Health Alert: The Surgeon General Sounding the Alarm on Skin Cancer

Now, we turn to the urgent new call to action from America's top doctor, the surgeon general. He is sounding an alarm about something we see all around us. Skin cancer. And he's doing it at the height of summer when a lot of the damage is being done. ABC's chief medical editor Dr. Richard Besser on the reason for this new urgency tonight. Reporter: This is what the surgeon general's call to action is trying to combat. Skin, sun and a deadly problem. Over the last 35 years, we've had a tripling of the cases of melanoma in this country. Reporter: In previous generations, it was the surgeon general leading the charge against smoking. Today's message? Avoid all forms of tanning. That's because skin cancer is now the single most common cancer in America. 5 million treated a year. And it's deadliest form, melanoma, is now the only common cancer in America that's on the rise. America's surgeon general is also a dermatologist. There's no such thing as a good tan. Tanned skin is damaged skin. It's a sign of excessive ultraviolet exposure. Reporter: Just look at the sun damage revelead in these uv filtered photos of skin that looks perfectly healthy. All those spots? Permanent alterations in the lowest layers of skin. For children, the sun is especially dangerous. We now know a blistering sunburn in childhood more than doubles the chance of melanoma later in life. So, listen to the surgeon general. Reduce indoor tanning. And you should be using one ounce of sunscreen every two hours, which means a family our four spending the day at the beach should use an entire 12 ounce container of lotion. The warning isn't just for the fair skinned. We're finding more and more skin cancers in hispanic populations, as well as african-american populations. And the reality is, this is becoming a publichealth crisis for the whole population. And rich Besser is here now. I want to go back to that sentence again. One blistering sunburn in childhood doubles the risk later? Reporter: It does. The risk still remains low, but that's frightening. Think about it this way. Every one of those sunburns you prevent helps keep the risk low. And this is difficult for me, as well, as Americans, we have to give up on the tan. It's just too dangerous. Give up on the tan. This is a big change tonight.

This transcript has been automatically generated and may not be 100% accurate.

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